1. Field of the Invention
This invention relates to an optical data form reading apparatus for reading an optical data form such as bar code data.
2. Description of the Prior Art
Optical data form reading apparatuses for reading an optical data form such as bar code data are known. FIG. 8 is a partial sectional plan view of a prior art illumination system for a bar code reader, and FIG. 9 is a perspective view of a prior art cylindrical lens 2 for projecting illumination light on a label having bar codes thereon. The cylindrical lens 2 has the same curvature R along the curved surface of the cylindrical lens 2 as shown in FIG. 9. Distances between the LEDs 1 and the cylindrical lens 2 vary in the LED arranging direction. Accordingly, the projected light pattern E is spread in the direction perpendicular to the LED arranging direction as shown in FIG. 10.
Japanese patent application provisional publication No. 9-128473 discloses another prior art optical data form reading apparatus as a bar code reader. FIG. 11 is a perspective view, partly a cut view, of this prior art bar code reader. FIG. 12 is a sectional view of the cylindrical lens 118 for this prior art bar code reader. The cylindrical lens 118 has a curved surface 117 as shown in FIG. 12. The curved surface 117 has successive three curvatures a, b, and c on the sectional plane in FIG. 12 to condense light from the LEDs 116 to adjust an illumination pattern to the reading area. However, the shape of the sectional area does not vary along the axis 119 of the cylindrical surface 117.
The aim of the present invention is to provide a superior optical data form reading apparatus.
According to the present invention, a first aspect of the present invention provides an optical data form reading apparatus comprising an objective lens; an optical sensor having a plurality of photosensitive elements arranged in a first direction which is perpendicular to an optical axis defined by said objective lens; a light emitting means for emitting illumination light; and a projection lens for condensing and projecting said illumination light on a readable target, said objective lens focusing reflected light from said readable target onto said optical sensor to generate an optical detection signal from said optical sensor, wherein said projection lens has at least a convex surface having curvature in a second direction which varies in said first direction to make said illumination light substantially collimated regarding said second direction along said projection lens in said first direction, and said second direction is perpendicular to said first direction and said optical axis.
According to the present invention, a second aspect of the present invention provides an optical data form reading apparatus based on the first aspect, wherein said light emitting means includes a plurality of light emitting elements arranged in said first direction beside said optical axis, said projection lens is arranged between said light emitting means and a reading plane of said readable target and extends in a third direction which is inclined to said optical axis, said convex surface curves only in said second direction, and said curvature just in front of each of said light emitting elements provides a focus point substantially at each of said light emitting elements.
According to the present invention, a third aspect of the present invention provides an optical data form reading apparatus based on the second aspect, wherein said projection lens has a flat surface on the side of said light emitting means and said convex surface at the other side, said convex surface curves only in said second direction, if it is assumed that said curvature at each point on said convex surface is Ra, a refraction index of said projection lens is n, and a focal distance at each point is f, (1/f)=(nxe2x88x921)(1/Ra).
According to the present invention, a fourth aspect of the present invention provides an optical data form reading apparatus comprising: an objective lens; an optical sensor having a plurality of photosensitive elements arranged in a first direction which is perpendicular to an optical axis defined by said object lens; a light emitting linear array including a plurality of light emitting elements arranged in said first direction for emitting illumination light; and a projection lens for condensing and projecting said illumination light on a readable target, said objective lens focusing reflected light from said readable target onto said optical sensor to generate an optical detection signal from said optical sensor, wherein said projection lens has at least a convex surface having curvature in a second direction varies in said first direction to make said illumination light substantially collimated regarding said second direction along said projection lens in said first direction, and said second direction is perpendicular to said first direction and said optical axis.
According to the present invention, a fifth aspect of the present invention provides an optical data form reading apparatus based on the fourth aspect, wherein said projection lens is arranged between said light emitting linear array and a reading plane of said readable target and extends in a third direction which is inclined to said optical axis, said convex surface curves only in said second direction, and said curvature just in front of each of said light emitting elements provides a focus point substantially at each of said light emitting elements.
According to the present invention, a sixth aspect of the present invention provides an optical data form reading apparatus based on the fifth aspect wherein said projection lens has a flat surface on the side of said light emitting array and said convex surface at the other side, said convex surface curves only in said second direction, if it is assumed that said curvature at each point on said convex surface is Ra, a refraction index of said projection lens is n, and a focal distance at each of said places is f, (1/f)=(nxe2x88x921)(1/Ra).
According to the present invention, a seventh aspect of the present invention provides an optical data form reading apparatus comprising an objective lens; an optical sensor having a plurality of photosensitive elements arranged in a first direction which is perpendicular to an optical axis defined by said object lens; light emitting means including a plurality of light emitting elements arranged in said first direction for emitting illumination light; and condensing means for condensing and projecting said illumination light on optical data form, said objective lens focusing reflected light from said optical data form onto said optical sensor to generate an optical detection signal indicative of said optical data form from said optical sensor, wherein said projection lens has at least a convex surface having curvature in a second direction varies in said first direction to make said illumination light substantially collimated such that a width an illuminated pattern on a reading plane of said optical data form in said second direction is substantially constant, and said second direction is perpendicular to said first direction and said optical axis.
According to the present invention, an eighth aspect of the present invention provides an optical data form reading apparatus based on the seventh aspect, wherein said light emitting means is arranged beside said optical axis, said projection lens is arranged between said light emitting means and a reading plane of said optical data form and extends in a third direction which is inclined to said optical axis, said convex surface curves only in said second direction, and said curvature just in front of each of said light emitting elements provides a focus point substantially at each of said photosensitive element.
According to the present invention, a ninth aspect of the present invention provides an optical data form reading apparatus based on the eighth aspect, wherein said projection lens has a flat surface on the side of said light emitting means and said convex surface at the other side, said convex surface curves only in said second direction, if it is assumed that said curvature at each point on said convex surface is Ra, a refraction index of said projection lens is n, and a focal distance at each of said places is f, (1/f)=(nxe2x88x921)(1/Ra).